University of California marine scientist David Valentine has made a shocking discovery, 3,000 feet below the ocean’s surface just ten miles off the coast of Los Angeles: “countless” barrels of toxic waste, laced with DDT, as CBS reports.

DDT is an odorless compound that was originally developed as an insecticide during World War II. In the 1960s, the compound was found to be highly toxic to both humans and animals, with the Environmental Protection Agency now labeling it as a “probable human carcinogen.”

The newly discovered barrels had been lying hidden there since the 1940s. We also still don’t know how far-reaching the environmental damage will be. A recent study found that one in every four adult sea lions in the region had developed cancer.

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With the help of an autonomous robotic submarine, Valentine came across the barrels between Long Beach and Catalina Island. It’s still unclear just how many there are, but some accounts estimate there be as many as half a million barrels, according to CBS.

Read more: Futurism